1. Field of the Invention
The present invention relates to a semiconductor device with circuits constructed of thin-film transistors (referred to TFT hereinafter). More particularly, the present invention relates to electro-optical equipment typified by liquid crystal display devices and EL (electroluminescence) display devices, and to semiconductor circuits. The present invention relates also to electrical equipment (or electronic equipment) with the electro-optical equipment or semiconductor circuits according to the present invention.
The term xe2x80x9csemiconductor devicexe2x80x9d as used in this specification embraces any and all devices which function by utilizing the characteristics of semiconductors. They include electro-optical equipment, semiconductor circuits, and electrical equipment.
2. Description of the Related Art
By virtue of its ability to be formed a transparent substrate, the thin film transistor (referred to as TFT hereinafter) has been actively investigated for its application to the liquid-crystal display of active matrix type (referred to as AM-LCD hereinafter). On account of its high mobility, the TFT made with crystalline semiconductor film (typically polysilicon film) is expected to display fine images if functional circuits are integrated on the same substrate.
AM-LCD is basically constructed of a pixel portion (or pixel matrix circuit) to display images, a gate driving circuit (or gate driver circuit) to drive TFT for each pixel arranged in the pixel portion, a source driving circuit (or source driver circuit) to send image signals to TFT for each pixel, and a data driving circuit (or data driver circuit), all of which are formed on the same substrate. Incidentally, the region in which the gate driving circuit and source driving circuit are formed is called the driving circuit portion.
Recently, the system-on-panel has been proposed which has, in addition to the pixel portion and driving circuit portion, signal processing circuits, such as signal driving circuits and xcex3-correction circuits, formed on the same substrate.
However, it is difficult to meet all the circuit requirements with TFT of the same structure because the pixel portion and the driving circuit portion differ from each other in their performance required. In other words, the driving circuit portion containing shift register circuits attaches importance to high operation, while the TFT constituting the pixel portion (referred to as pixel TFT) attaches importance to the high withstanding voltage. So far, there has been no TFT structure to satisfy both of them.
The present applicant filed an application for construction which is characterized in that the TFT constituting the driving circuit portion (referred to as driving TFT hereinafter) and the pixel TFT differ from each other in the thickness of the gate insulating film. (Japanese Patent Laid-open No. 10-056184 and its corresponding to U.S. patent application No. 08/862,895) To be concrete, the gate insulting film of the driving TFT is made thinner than the gate insulating film of the pixel TFT.
The present invention is an improvement on the pixel portion which is based on the construction disclosed in the above-mentioned official gazette. To be concrete, it is an object of the present invention to provide a construction to secure a large capacity in a small area.
It is another object of the present invention to provide an electro-optical equipment with high reliability (typified by AM-LCD) in which each circuit is constructed of TFT of adequate structure suitable for individual circuits. It is another object of the present invention to provide a semiconductor device (electrical equipment) with high reliability which has the electro-optical device as the display part.
The first aspect of the present invention resides in a semiconductor device of the type in which the pixel portion has a pixel TFT and a storage capacitance for each pixel, characterized in that said pixel TFT has an active layer which is formed above a light blocking film, with an insulating film of two or more laminated layers interposed between them, said storage capacitance is composed of an electrode (which is formed in the same layer as said light blocking film), a dielectric material, and a semiconductor film (of the same composition as the drain region of said pixel TFT), and said dielectric material is a partial layer of said insulating film of two or more laminated layers.
The second aspect of the present invention resides in a semiconductor device of the type in which the pixel portion has a pixel TFT and storage capacitance for each pixel, characterized in that said pixel TFT has an active layer which is formed above a light blocking film, with an insulating film of two or more laminated layers interposed between them, said storage capacitance is composed of an electrode (which is formed in the same layer as said light blocking film), a dielectric material, and a semiconductor film (of the same composition as the drain region of said pixel TFT), and said dielectric material is said insulating film of two or more laminated layers remaining after removal of a portion thereof.
The third aspect of the present invention resides in a semiconductor device of the type in which the pixel portion has a pixel TFT and a storage capacitance for each pixel, characterized in that said pixel TFT has an active layer which is formed above a light blocking film, with a first insulating film (in contact with the light blocking film) and a second insulating film (in contact with said active layer) interposed between them, and said storage capacitance is composed of an electrode (which is formed in the same layer as said light blocking film), said second insulating film, and a semiconductor film (of the same composition as the drain region of said pixel TFT).
The semiconductor device defined above in the third aspect is characterized in that said second insulating film has a thickness which is preferably smaller than ⅕ (preferably {fraction (1/100)} to {fraction (1/10)}) of that of the laminate film composed of said first insulating film and second insulating film.
The fourth aspect of the present invention resides in a process for producing a semiconductor device in which the pixel portion has a pixel TFT and a storage capacitance for each pixel, said process comprising a step of forming on a substrate a light blocking film and an electrode from the same material as the light blocking film, a step of forming a first insulating film that covers said light blocking film and said electrode, a step of etching said first insulating film, thereby forming an opening on said electrode, a step of covering said first insulating film and said opening, thereby forming a second insulating film, and a step of forming a semiconductor film on said second insulating film.
The fifth aspect of the present invention resides in a process for producing a semiconductor device in which there is a driving circuit portion and the pixel portion has a pixel TFT and a storage capacitance for each pixel, said process comprising a step of forming on a substrate a light blocking film and an electrode from the same material as the light blocking film, a step of forming a first insulating film that covers said light blocking film and said electrode, a step of etching said first insulating film, thereby forming an opening on said electrode, a step of covering said first insulating film and said opening, thereby forming a second insulating film, a step of forming a semiconductor film on said second insulating film, a step of covering said semiconductor film, thereby forming a gate insulating film, a step of etching a part of said gate insulating film, thereby exposing the semiconductor film of said driving circuit portion and a part of the semiconductor film of said pixel portion, and a step of performing thermal oxidation, thereby forming a thermally oxidized film on the surface of the semiconductor film which has been exposed by the etching of said gate insulating film.
The sixth aspect of the present invention resides in a process for producing a semiconductor device in which there is a driving circuit portion and the pixel portion has a pixel TFT and a storage capacitance for each pixel, said process comprising a step of forming on a substrate a light blocking film and an electrode from the same material as the light blocking film, a step of forming a first insulating film that covers said light blocking film and said electrode, a step of etching said first insulating film, thereby forming an opening on said electrode, a step of covering said first insulating film and said opening, thereby forming a second insulating film, a step of forming a semiconductor film on said second insulating film, a step of covering said semiconductor film, thereby forming a gate insulating film, a step of etching a part of said gate insulating film, thereby exposing the semiconductor film of said driving circuit portion and a part of the semiconductor film of said pixel portion, a step of performing thermal oxidation, thereby forming a thermally oxidized film on the surface of the semiconductor film which has been exposed by the etching of said gate insulating film, and a step of forming the LDD region in the semiconductor film of said driving circuit portion and the semiconductor film of said pixel portion, such that the LDD region in said driving circuit portion differs in length from that in said pixel portion.